The following description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed inventions, or that any publication specifically or implicitly referenced is prior art.
17-allylamino-geldanamycin (17-AAG) is a synthetic analog of geldanamycin (GDM). Both molecules belong to a broad class of antibiotic molecules known as ansamycins. GDM, as first isolated from the microorganism Streptomyces hygroscopicus, was originally identified as a potent inhibitor of certain kinases, and was later shown to act by stimulating kinase degradation, specifically by targeting “molecular chaperones,” e.g., heat shock protein 90s (HSP90s). Subsequently, various other ansamyins have demonstrated more or less such activity, with 17-AAG being among the most promising and the subject of intensive clinical studies currently being conducted by the National Cancer Institute (NCI). See, e.g. Federal Register, 66(129): 35443-35444; Erlichman et al., Proc. AACR (2001), 42, abstract 4474.
HSP90s are ubiquitous chaperone proteins that are involved in folding, activation and assembly of a wide range of proteins, including key proteins involved in signal transduction, cell cycle control and transcriptional regulation. Researchers have reported that HSP90 chaperone proteins are associated with important signaling proteins, such as steroid hormone receptors and protein kinases, including, e.g., Raf-1, EGFR, v-Src family kinases, Cdk4, and ErbB-2 (Buchner J., 1999, TIBS, 24: 136-141; Stepanova, L. et al., 1996, Genes Dev. 10: 1491-502; Dai, K. et al., 1996, J. Biol. Chem. 271: 22030-4). Studies further indicate that certain co-chaperones, e.g., Hsp70, p60/Hop/Sti1, Hip, Bag1, HSP40/Hdj2/Hsj1, immunophilins, p23, and p50, may assist HSP90 in its function (see, e.g., Caplan, A., 1999, Trends in Cell Biol., 9: 262-68).
Ansamycin antibiotics, e.g., herbimycin A (HA), geldanamycin (GM), and 17-AAG are thought to exert their anticancerous effects by tight binding of the N-terminus pocket of HSP90 (Stebbins, C. et al., 1997, Cell, 89: 239-250). This pocket is highly conserved and has weak homology to the ATP-binding site of DNA gyrase (Stebbins, C. et al., supra; Grenert, J. P. et al, 1997, J Biol. Chem., 272: 23843-50). Further, ATP and ADP have both been shown to bind this pocket with low affinity and to have weak ATPase activity (Proromou, C. et al, 1997, Cell, 90: 65-75, Panaretou, B. et al., 1998, EMBO J, 17: 4829-36). In vitro and in vivo studies have demonstrated that occupancy of this N-terminal pocket by ansamycins and other HSP90 inhibitors alters HSP90 function and inhibits protein folding. At high concentrations, ansamycins and other HSP90 inhibitors have been shown to prevent binding of protein substrates to HSP90 (Scheibel, T., H. et al., 1999, Proc. Natl. Acad. Sci. USA 96: 1297-302; Schulte, T. W. et al., 1995, J. Biol. Chem. 270: 24585-8; Whitesell, L., et al., 1994, Proc. Natl. Acad. Sci. USA 91: 8324-8328). Ansamycins have also been demonstrated to inhibit the ATP-dependent release of chaperone-associated protein substrates (Schneider, C., L. et al., 1996, Proc. Natl. Acad. Sci. USA, 93: 14536-41; Sepp-Lorenzino et al., 1995, J. Biol. Chem. 270: 16580-16587). In either event, the substrates are degraded by a ubiquitin-dependent process in the proteasome (Schneider, C., L., supra; Sepp-Lorenzino, L., et al., 1995, J. Biol. Chem., 270: 16580-16587; Whitesell, L. et al., 1994, Proc. Natl. Acad. Sci. USA, 91: 8324-8328).
This substrate destabilization occurs in tumor and non-transformed cells alike and has been shown to be especially effective on a subset of signaling regulators, e.g., Raf (Schulte, T. W. et al., 1997, Biochem. Biophys. Res. Commun. 239: 655-9; Schulte, T. W., et al., 1995, J. Biol. Chem. 270: 24585-8), nuclear steroid receptors (Segnitz, B., and U. Gehring. 1997, J. Biol. Chem. 272: 18694-18701; Smith, D. F. et al., 1995, Mol. Cell. Biol. 15: 6804-12), v-src (Whitesell, L., et al., 1994, Proc. Natl. Acad. Sci. USA 91: 8324-8328) and certain transmembrane tyrosine kinases (Sepp-Lorenzino, L. et al., 1995, J. Biol. Chem. 270: 16580-16587) such as EGF receptor (EGFR) and Her2/Neu (Hartmann, F., et al., 1997, Int. J. Cancer 70: 221-9; Miller, P. et al., 1994, Cancer Res. 54: 2724-2730; Mimnaugh, E. G., et al., 1996, J. Biol. Chem. 271: 22796-801; Schnur, R et al., 1995, J. Med. Chem. 38: 3806-3812), CDK4, and mutant p53. Erlichman et al., Proc. AACR (2001), 42, abstract 4474. The ansamycin-induced loss of these proteins leads to the selective disruption of certain regulatory pathways and results in growth arrest at specific phases of the cell cycle (Muise-Heimericks, R. C. et al., 1998, J. Biol. Chem. 273: 29864-72), and apoptsosis, and/or differentiation of cells so treated (Vasilevskaya, A. et al., 1999, Cancer Res., 59: 3935-40).
Ansamycins thus hold great promise for the treatment and/or prevention of many types of cancers and proliferative disorders. However, at present the various known methods of producing ansamycins exhibit one or more of low yield, low purity, instability, environmental toxicity associated with the use of halogenated organic solvents, and additional attendant costs in terms of time, expense, waste disposal, and health risks to those taking the drugs so made. Examples of known methods include Sasaki et al, U.S. Pat. No. 4,261,989, assigned to Kaken Chemical Co, Ltd., which reports the synthesis of various ansamycin derivatives, including 17-AAG, using various organic solvents and tedious extraction techniques, and Schnur et al, U.S. Pat. No. 5,932,566 and PCT/IB94/00160 (WO 95/01342), assigned to Pfizer Inc., which describe similar processes.
It is an object of the invention to improve one or more of the shortcomings of the existing art, i.e., ameliorate one or more of low yield, low purity, instability, environmental toxicity associated with the use of halogenated organic solvents, and additional attendant costs in terms of time, expense, waste disposal, and health risks.